Why does my main house consumer unit trip when the inverter switched to AC backup?

[marconi]

Mea culpa maxima. I have confused you with Lewis Curle's electrical problem I am also working on who does have a new baby. What an idiot I am!

What town in Somerset?

 

[marconi]

Just found this by a google search - this problem is not new to Voltacon Ltd.

TN-S Earthing for Off Grid Inverter. Neutral-Ground Bonding - Voltacon Solar Blog - https://voltaconsolar.com/blog/knowledge-base/tn-s-earthing-for-off-grid-inverter-neutral-ground-bonding/

Re your #56: If look at the link above you will see some commentary on making an NE link inside the Voltacon badged inverter. Note the Voltacon and similar inverters with a different badge on (except Axpert) have the option of making an NE link inside the inverter box.

The Axpert badged inverter appears to have an internal NE link as standard. We could then open up this box and disconnected the internal link and make it outside the box. If we did this then we could put a double pole contactor immediately after the Axpert box's ac output terminals but before this outside NE link which is opened before the inverter enters line/bypass mode. Thus the ac input's N and E would not be bridged any longer by an output side NE link because the output N is interrupted by the double pole contactor opening. Now in bypass/line mode and during charging there would only be an NE link before your main DB's MEM RCD as is usual. When charging finishes, bypass/line mode is turned off the inverter output would be reconnected to the ac output socket by closing the dp contactor. To maintain the manufacturer's warranty we could ask Voltacon Ltd to disconnected the internal NE link when you return the Axpert box to them.

At no time would both input and output Ns be connected nor of course the input and output Ls. The input and out Es however would remain connected - a good thing.

If you wanted the mains to be connected to your off grid DB during charging periods we can arrange this by a transfer switch which swaps between mains LN and inverter LN under control of a signal we can produce as required. The box has some no volt contacts I am pretty sure we can co-opt to produce the signal.

Or by something along these lines it can be done and be compliant and safe.

The other option is to return the Axpert box and exchange it for a Voltacon box which indeed is normally the standard offering inside the SP5048 off gird plug and play cabinet as it does not have the internal NE link ready made. But of course we would check that this was so before with Voltacon and you did the exchange.

Silent Power SP5048, Off Grid Inverter Charger Kit 5000Watt, PLUG 'N' PLAY PHOTOVOLTAIC CONTROL CABINET - https://voltaconsolar.com/off-grid-kits/48v-off-grid/silent-power-sp5048-off-grid-photovoltaic-cabinet.html?utm_medium=cpc&utm_source=google&gclid=Cj0KCQiA3eGfBhCeARIsACpJNU_RBSwKstC74YG-s9Oih5QepkwYLqdIkArLrQJQ753gPymD3-_V40oaAvLKEALw_wcB

The use of a Voltacon box in lieu of an Axpert looks very promising because I also found this product by Voltacon, an off grid inverter controlled grounding/earthing kit,which it looks very much like is a ready made design to do some of what I mentioned in the second paragraph above:

Grounding Box for Off Grid Inverters - https://voltaconsolar.com/off-grid-inverter-grounding-tns.html

A bit confusing though 'cos it mentions Axpert boxes rather than Voltacon ones which we are pretty sure the former already have the NE link done inside so I need to read up and clarify with Voltacon next week.

As clear as mud? I hope not. Ask if it is not clear to you. I should do a drawing but it is too early in the morning right now.

 

[marconi]

Hello again Marconi

I followed the instructions and got the AC to charge the batteries with the USB timer set and it was charging for a short while.
I followed the instructions one at a time and then turned on the Solar Consumer unit. I then ran a kettle on the kitchen circuit and the microwave on a separate circuit serving the extension this took the output to 3Kw so I added an induction hob which took the output to 5.1 Kw, the max of this inverter being 5.5Kw I believe.

At this point the MEM rcd has not tripped and until I get another couple of sockets added to the next MCB circuit I can only add to the two I have at present with more items. I am surprised the mem did not trip but this may be as a result of only 2 mcb currently pulling power through the consumer unit.

Let me know your thoughts regarding this test and I look forward to trying some more experiments before I remove the unit to return to the supplier.
I have been testing all of my pv wiring in a last ditch attempt to see what is causing my dc.dc overcurrent issue but with no obvious problems with the wiring I am resigned to returning it to the supplier next week.

regards and thanks as ever for the help

Tonyboy

Is the cabinet earthed back to the main db earth bar? Ie is the earth bar connected the the earth of the ac input c form socket?

 

[marconi]

Latest email to Voltacon Ltd including these three links:

To: [email protected];
27/02/2023 07:23
1


Axpert Inverter - Who has stock - Page 5 - https://www.4x4community.co.za/forum/showthread.php/223750-Axpert-Inverter-Who-has-stock/page5

TN-S Earthing for Off Grid Inverter. Neutral-Ground Bonding - Voltacon Solar Blog - https://voltaconsolar.com/blog/knowledge-base/tn-s-earthing-for-off-grid-inverter-neutral-ground-bonding/

Grounding Box for Off Grid Inverters - https://voltaconsolar.com/off-grid-inverter-grounding-tns.html

Dear

Good morning. I wondered if have had time to consider what I sent you? With further research and testing of the Axpert MKS iv 5kW solar inverter fitted in my clients SP5048 off-grid plug and play panel I pretty convinced in my own mind that the tripping of the up-front RCD is because there is an N-E link made inside the Axpert box. Interestingly, I have discovered that for the equivalent (same?) Voltacon or Conversol branded solar inverter there is no internal N-E link. Instead one can buy this unit which makes the N-E link externally whenever the inverter is supplying the output, otherwise ie in bypass mode it is disconnected because the N-E link is made upstream from the supply. Perhaps you could review the links above for me please?

Regards

 

[Tonyboy]

Is the cabinet earthed back to the main db earth bar? Ie is the earth bar connected the the earth of the ac input c form socket?

Good morning Marconi.

I have a few issues with my parents currently so I am in and out a lot and may take some time to respond.

I will try to answer all of the posts in one go and if I miss something let me know. I fear it will be a long post!

I am near Glastonbury in Somerset.

Your detailed explanation regarding the NE link and more was fine.

RE the inverter supplied. I was expecting the Voltacon V7 box in my cabinet not the Axpert and I have not raised this issue with them yet (but I will be this week). The information you have provided RE the earth link in the axpert and the completely unmentioned to me, by Voltacon, earth grounding box (which I will also assume should have been provided in the cabinet if the axpert is wired as you have outlined in the detailed paragraph above).

I have no desire to have the incoming supply connected to my pv sockets so the transfer switch will not be required.
Ironically I did make it quite clear to Voltacon prior to purchase, exactly what I required and when the box arrived with the Axpert in I foolishly assumed they has replaced the voltacon V7 to achieve the required parameters I had detailed. i.e. no mains supply to appliances via the cabinet and charging from the mains at night on cheap rate electricity. (How foolish)

I am still working through the issue of the pv input at the inverter putting out voltage when it is on and connected to the panels. as well as getting voltage on the earth from the array rails on the roof.

This morning I have bypassed all of the cabinet connections and made direct connections to the inverter from my pv double pole isolator before the cabinet and this made no difference. I did this in case something was incorrectly wired in the cabinet.
Given my limited knowledge of inverters I can only assume that the pv input of the inverter actually putting out voltage is perhaps why I get the f12 dc.dc overcurrent fault. And if they are not supposed to be outputting voltage from an input, I am fairly certain the inverter is at fault. I hope that this is not going to or has already caused damage to any of the panels I have.

The somewhat more concerning fact is that when I put the N wire of my multi meter (only N) on the earth cable from the roof mounting brackets in the cupboard before the earth bus bar and get 130 or more volts on the meter has led me to disconnect it form the ground rod in case it is going to damage the 2 pylontech batteries already connected to the earth rod.
The array earth and the battery earth were connected via a bus bar to the ground rod so at present it has the batteries only connected. It is almost as if the voltage is being induced into the earth cable but I can't figure out how.

The cabinet has what looks like copper earth connection points/bolts on the inside as well as earth bonding across from the door to the body of the cabinet. I do not have an earth connection between the cabinet body and the earth on the ac input on the c plug connections. And with the voltage being present on the earth from roof array I do not have the array connected to the earth either. for fear of setting up a loop somewhere on the cabinet or the batteries or both.

I have not disconnected the inverter yet as time does not permit currently, but I will be contacting Voltacon this week with a view to getting my money back on what seems to be a faulty inverter that was installed in the cabinet and I believe was completely untested before it arrived with me.

Incidentally if you were supplied a cabinet as described would you expect it to have a plate or some such detailing its serial number and when and who tested it prior to dispatch? As I have received no information at all from Voltacon despite numerous requests and being told the cabinet should have come with a DVD from the engineer who built it. The cabinet came with a delivery note only and there are no company badges (Voltacon) on the inverter or the cabinet itself let alone a serial number/product number by which to identify it.
Subsequently when I asked for this again I was told they could not make a DVD for every cabinet they made.

With regards to the baby, do not worry at all, it seems like you are very active helping people and I am sure if I was in your position I would make far more and much worse mistakes.

As ever thanks for the help and advice.

Regards

Tonyboy

 

[marconi]

Thank you. I will study over the next day or so. I am in email dialogue with V Ltd but making slow (no) progress. I have copied you PM the latest emails which change the tone a little to indicate I am not getting the thinking and answers I want from them. For this reason they are not in the public domain.

It would be a return trip of 7 hours to visit you from where I live. If I decided to visit and you agreed would you pay the diesel (Ford Galaxy 50mpg on a long run)?

 

[marconi]

I think those voltage measurements are unsurprising but to be sure would you draw me a diagram which shows accurately what each earth terminal is connected to and between?

Also show how you made your voltage measurements and the readings. I normally do this by a V in a circle with two leads from it to the two points across which I measure a voltage.

The F12 fault could indeed be due to an pv over voltage measurement. But, I think you said the system functions normally even with F12? This over voltage could be a result of the way the earths are connected and to what hence my first paragraph.

 

[Tonyboy]

I think those voltage measurements are unsurprising but to be sure would you draw me a diagram which shows accurately what each earth terminal is connected to and between?

Also show how you made your voltage measurements and the readings. I normally do this by a V in a circle with two leads from it to the two points across which I measure a voltage.

The F12 fault could indeed be due to an pv over voltage measurement. But, I think you said the system functions normally even with F12? This over voltage could be a result of the way the earths are connected and to what hence my first paragraph.

Good morning Marconi

I will try to get the measurements done today if possible and send you a picture of the results.

The F12 fault is a dc.dc overcurrent fault as opposed to an overvoltage fault and voltage of the 7 panels is 256V well below the max of 500v limit on the inverter. I will double check the two sets of panels and ensure they are producing the correct voltage from each in the meantime.

I did notice from re reading the manual that the axpert is a non isolating inverter and there are limits to the type of panels that can be connected to it, fortunately I have the single (mono) crystalline) type that it says are fine, It also mentions that the panels are not supposed to be grounded to the inverter. This did make me wonder how you are supposed to ground the solar panel rails etc. There is only mention of connecting the + and - from the PV to the cabinet and I cannot find any recommendations regarding the grounding of the pv array on the V site. This was why I have not connected the earth cable from the array to the cabinet or the ground rod at present. And since finding voltage on the earth cable it has made me reluctant to connect it to anything until I know where this is from.
The irony is also that the manual states the inverter should be connected to a permanent grounded wiring system and I have no idea if this is achieved in the way the cabinet and controls are wired before it is dispatched, or this is something that also needs to be done before it is fit to use.
The details on the V site indicate connection of pv, battery and c plugs is all that is required.
I will reply as soon as I am able.

Many thanks as ever

Regards Tonyboy

 

[marconi]

Please send me a link to what you have read on earthing on the V Ltd website. The earthing and bonding of your installation is something we need to get right mindful that your supply is PME which has restrictions on using the Main Earth Terminal (MET) outside the 'equipotential zone' generally and simply understood in the domestic setting as anything within the home.

 

[Tonyboy]

Please send me a link to what you have read on earthing on the V Ltd website. The earthing and bonding of your installation is something we need to get right mindful that your supply is PME which has restrictions on using the Main Earth Terminal (MET) outside the 'equipotential zone' generally and simply understood in the domestic setting as anything within the home.

Hello Marconi
The only items on their web site refer to the grounding on generators as far as I can see, however the manual for the Axpert states:
GROUNDING INSTRUCTIONS -This inverter/charger should be connected to a permanent grounded wiring system. Be sure to comply with local requirements and regulation to install this inverter and in a separate paragraph below this it says
"to avoid malfunctions do not connect any pv module with possible current leakage to the inverter, for example a grounded pv module will cause current leakage to the inverter. When using cigs modules please be sure no grounding".

I will complete the drawing today or in the morning tomorrow and send it over, I may well send it pm and include some pictures of the test points.

I do not have the system connected to a ground at present as it is not working anyway, with the exception of the batteries connected to the ground rod. I had intended to keep all of the solar separate from the rest of the supply to the house and this included all of the connections back to the cu with the exception of the temporary supply for the overnight when required. I had not intended to use the incoming supply earth connection.

I will send the pictures as soon as I am able

Regards and thanks

Tonyboy

 

[Tonyboy]

Please send me a link to what you have read on earthing on the V Ltd website. The earthing and bonding of your installation is something we need to get right mindful that your supply is PME which has restrictions on using the Main Earth Terminal (MET) outside the 'equipotential zone' generally and simply understood in the domestic setting as anything within the home.

 

[Tonyboy]

Please send me a link to what you have read on earthing on the V Ltd website. The earthing and bonding of your installation is something we need to get right mindful that your supply is PME which has restrictions on using the Main Earth Terminal (MET) outside the 'equipotential zone' generally and simply understood in the domestic setting as anything within the home.

Hi Marconi

I think I have slipped up in the reply, it should have accompanied the message I sent before about adding a drawing, so I have replied in this message. I have attached a couple of pictures of the points I took my measurements for the earth and PV which I have somewhat rudiment ally marked with my mouse, I have added a short description to go with it to clarify the drawings.

The first measurement on the pv string input of 246vdc is with the inverter off and the main isolator from the roof on.
The second is measured at the same point on the pv input is with the inverter on and the isolator from the roof on.
The earth is measured at the earth bus bar in the cupboard, it is the cable from the pv array and rails on the roof and the bus bar is not connected to the earth rod as I have issues with connecting a cable showing 130vdc + to the earth rod that the two pylontech batteries are connected to.
Hope this makes sense.
Let me know if you require any more information and many thanks as ever

Tonyboy

 

[marconi]

Have you reported the state of the inverter on/off correctly for voltages 1 and 2 above? I would expect voltage 2 when the inverter is off to be round about 7 x 50 = 350V and voltage 1 when the inverter is on and MPPT operating to be lower eg your reading of 246V. The open circuit voltage of a panel is about 50V.

The 130-170V reading of the array metalwork to earth rod is to be expected due to the distributed insulation resistance of the panels and cabling to ground. For evenly distributed insulation resistance to earth the voltages would be half the +ve to -ve voltages so 350/2 = 175V and 246/2 = 123V - near enough what you measured.

 

[Tonyboy]

Have you reported the state of the inverter on/off correctly for voltages 1 and 2 above? I would expect voltage 2 when the inverter is off to be round about 7 x 50 = 350V and voltage 1 when the inverter is on and MPPT operating to be lower eg your reading of 246V. The open circuit voltage of a panel is about 50V.

The 130-170V reading of the array metalwork to earth rod is to be expected due to the distributed insulation resistance of the panels and cabling to ground. For evenly distributed insulation resistance to earth the voltages would be half the +ve to -ve voltages so 350/2 = 175V and 246/2 = 123V - near enough what you measured.

Hello Marconi

With regards to the two readings. Reading 1 is the inverter off reading and it is derived from the open circuit voltage of the panels at 37.6 v each. When measured at the roof it was 253vdc which was a combination of the top string of 108 vdc and the lower of 145 vdc. At the isolator and input point on the cabinet it is 246vdc which I assumed was as a result of some loss in the cabling run from the roof to the cupboard.

The second reading is when the inverter is switched on and is between 268 and 391 vdc give or take. It does go up and down and I assume this is as a result of the mppt fault present in the inverter.

If I isolate the pv string and measure at the same point I am getting well over 100 vdc or more at the input to the inverter with no pv connected i.e. the input side to the inverter is showing a dc voltage output of this voltage. This is what is concerning me as I had assumed that there was no way for there to be an output present on the input to the inverter. My thoughts were that the mppt fault is something that is allowing voltage out when it should not be doing so, this output can only be derived from the batteries connected to the cabinet as at the point I measured the voltage the AC was off.

With regard to the earth cabling voltage reading from the array and panels, does this mean that it is safe to connect the earth cable to the ground rod then? I have the 2 batteries connected to this at present.
Am I correct thinking that the distributed insulation value is derived from or related to the grounding of the cables in the cabinet via the neutral to earth link that is present in the inverter.
I have not been able to find out very much regarding the earthing arrangement for the cabinet but as there is a line neutral and earth connection to both the input and output c plug sockets on the cabinet I was making (possibly incorrectly) the assumption that the cabinet and its contents is earthed back to my house hold consumer unit when it is plugged in to the AC input c plug.

I am very grateful for the time and trouble you have taken to assist me. Given that I thought I was buying something that is advertised as plug and play it seems currently to be anything but.

Please let me know if you wish me to measure anything else as I will gladly do so.

Regards

Tonyboy

 

[marconi]

To observe a voltage between the PV input terminals when the array is disconnected from them and the inverter is producing an ac output using power form the battery is normal. The solar inverter is transformerless which means there is no air gap between the dc inputs (PV and battery) and the ac output. Due to the way the dc input is converted to a higher voltage and then switched in polarity at the mains frequency and also the earthed output neutral there is an alternating voltage waveform ( square wave shaped ) impressed across the PV+ and PV- inputs. It is usual and nothing to worry about but of course don’t touch live connections!

The 130V dc ( circa half the end to end array voltage) between array metal work and an earth rod is normal when the insulation resistance is uniformly distributed from the plus to minus side of the array and neither the pv+ nor the PV- is connected to earth which they should not be. They are left floating.

You should connect the array metal work to a local earth rod so that the touch potential between the metal work and local ground is small.

I will provide further advice on earthing arrangements for the SP5048 cabinet in a later email.

Regarding the F12 fault code - does it occur in battery only mode, PV only or both battery and PV? Does it occur when the inverter is not supplying the ac output Load ? Does it occur when the battery is fully charged and not supplying any ac output load? Does it occur on switch on of the inverter or some while later? Does it occur when PV only is supplying a small low wattage load? Does it occur battery only supplying small wattage load?

 

[Tonyboy]

To observe a voltage between the PV input terminals when the array is disconnected from them and the inverter is producing an ac output using power form the battery is normal. The solar inverter is transformerless which means there is no air gap between the dc inputs (PV and battery) and the ac output. Due to the way the dc input is converted to a higher voltage and then switched in polarity at the mains frequency and also the earthed output neutral there is an alternating voltage waveform ( square wave shaped ) impressed across the PV+ and PV- inputs. It is usual and nothing to worry about but of course don’t touch live connections!

The 130V dc ( circa half the end to end array voltage) between array metal work and an earth rod is normal when the insulation resistance is uniformly distributed from the plus to minus side of the array and neither the pv+ nor the PV- is connected to earth which they should not be. They are left floating.

You should connect the array metal work to a local earth rod so that the touch potential between the metal work and local ground is small.

I will provide further advice on earthing arrangements for the SP5048 cabinet in a later email.

Regarding the F12 fault code - does it occur in battery only mode, PV only or both battery and PV? Does it occur when the inverter is not supplying the ac output Load ? Does it occur when the battery is fully charged and not supplying any ac output load? Does it occur on switch on of the inverter or some while later? Does it occur when PV only is supplying a small low wattage load? Does it occur battery only supplying small wattage load?

Hello Marconi and thanks for the reply

I will connect the earth from the pv rails and panels tomorrow, thanks for clearing up the question I posed.

Regarding the F12 fault. It originally occurred on Jan 29th when I had connected the batteries and the PV array as described in the V ltd directions. The batteries were at 49.0 vdc each and the array was producing 252 vdc if I remember correctly. It ran for a while producing about 400watts from the pv and then as far as I recall it went into the f12 fault.

I did not have any load connected as I was merely checking to see the inverter would charge the batteries from the PV.
This was at a point were I wanted to ensure the batteries were working and taking a charge etc.

The fault occurs whenever the inverter is in PV and battery mode I.e. I have the inverter set to provide power to the appliances from pv first then if not enough p.v the battery. That said I have not used the setup yet in any meaningful way as I am concerned about the issue of the inverter stopping on the F12 fault.

I can and have charged the batteries from the AC if I leave the solar consumer unit off and disconnect the ac out from the cabinet via the mcb/ rcd. (as we did in your experiment) I then just change the setup to USB and set the time to charge the batteries to full (so far this has only been 25%) as they were at about 75% when they arrived.

The fault seems to happen not long after I turn on the pv isolator and it shows the pv voltage and wattage on the front panel, soon after it starts to apply a charge to the batteries and then goes off on the fault. It seems to make a small bussing noise at the point it starts to charge and then soon after it goes to f12.
To clarify then, the inverter has not been charging the batteries when there has been an output load and the batteries are currently full. It did trip to F12 when charging the batteries and they were 75% and with no load applied.

It may be that I should try the charging again when we have some sunshine and I use some of the battery power beforehand and then turn on the pv with a small load applied to the solar output to the house? If this is a good idea I will probably need to wait a while as the weather here is overcast and forecast to be this week. I get very low wattage when it is like this so I will wait for a sunny day where I can apply a bit more to the inverter/batteries/load.

Many thanks and as ever I am very grateful.

Regards

Tonyboy

 

[marconi]

https://content.storefront7.co.za/s...56k48v/documents/rct-axpert-mks-iv-manual.pdf

see page 15 Program 2 - Maximum charging current (which is solar and utility currents). What do you have set? Try reducing maximum charging current. If it is set now to the default of 60A then reduce to 30A. If 40A then to 20A. ie whatever the max current set now then halve the current value. Then see if F12 happens when solar pv is charging battery.

 

[Tonyboy]

https://content.storefront7.co.za/s...56k48v/documents/rct-axpert-mks-iv-manual.pdf

see page 15 Program 2 - Maximum charging current (which is solar and utility currents). What do you have set? Try reducing maximum charging current. If it is set now to the default of 60A then reduce to 30A. If 40A then to 20A. ie whatever the max current set now then halve the current value. Then see if F12 happens when solar pv is charging battery.

Hello Marconi

I have had a look today and setting 02 is set to 10 amps by default for pylontech batteries setting number 05 .

I have the max ac charging current set to 10 amps as well. There is a note on setting 11 (ac charge current) regarding the setting in prog 2 stating that if setting in 2 is smaller than in 11 the inverter will apply charging current from 2 to the utility charger. There does not seem to be a way to reduce either of these settings further other than reduce the ac current to its minimum of 2 amps which seems like a very low setting for overnight charging. If this is an option I will surely try it if you think it will assist. At present the weather is overcast and no sun at all.

Many thanks as ever

Tonyboy

 

[marconi]

Thank you. As you say the charging current limits are already low at 10A so a very high charging current is not the cause of F12 as I mused it might be. I was 'hoping' you would say 60 to 120A!

Could you tell me the edition of software your Axpert inverter box is running please?

Are you or your wife musical? What frequency would you estimate the buzzing to be that you mentioned earlier? This site provides some tones to compare with:

 

[marconi]

Re: Program 13 page 19 'Setting voltage point back to battery mode when selecting “SBU” (SBU priority)' in program 01' of the manual reference in my #77 - what voltage do you have set as the threshold for point back?